Yes, you can buy stuff on Amazon using
BTC. There is a wallet called Ipayyou (it is 2 years old age now) that allows you to buy on Amazon using your bitcoins. The wallet has a featured called Amazon Direct that lets you transfer any dollar amount of bitcoin to use for purchases on Amazon. I might be mistaken but I think this is the only way, for now, to buy things on amazon using bitcoins.
For more information check:https://bitcoinexchangeguide.com/ipayyou/
or visit :
https://wallet.ipayyou.io/As a matter of fact Amazon already accept bitcoin as payment of their costumer. I think adding bitcoin in their payment method is another good strategy to their competitors. And, I think they notice that many people have bitcoin than paper money so they add it in their payment method.